磨料形貌及分散介质对4H碳化硅晶片研磨质量的影响研究

研磨作为4H碳化硅(4H-SiC)晶片加工的重要工序之一,对4H-SiC衬底晶圆的质量具有重要影响。本文研究了金刚石磨料形貌和分散介质对4H-SiC晶片研磨过程中材料去除速率和面型参数的影响,基于研磨过程中金刚石磨料与4H-SiC晶片表面的接触情况,推导出简易的晶片材料去除速率模型。研究结果表明,磨料形貌显著影响4H-SiC晶片的材料去除速率,材料去除速率越高,晶片的总厚度变化(TTV)越小。由于4H-SiC中C面和Si面的各向异性,4H-SiC晶片研磨过程中C面的材料去除速率高于Si面。在分散介质的影响方面：水基体系研磨液的Zeta电位绝对值较高,磨料分散均匀,水的高导热系数有利于控制研磨过程中的盘面温度;乙二醇体系研磨液的Zeta电位绝对值小,磨料易发生团聚,增大研磨过程的磨料切入深度,晶片的材料去除速率提高,晶片最大划痕深度随之增大。     

4H-SiC的强氧化液化学机械抛光

研究了一种新型的化学机械抛光方法,使用以KMnO4作为氧化剂的强氧化性化学机械抛光液(SOAS)进行化学机械抛光.研究了在4H-SiC硅面和碳面的化学机械抛光过程中,SOAS溶液中KMnO4的浓度对抛光质量的影响.使用原子力显微镜(AFM)和精密电子天平,分别测试了表面粗糙度和去除率.结果表明,适量的KMnO4可以大幅度提高4H-SiC的化学机械抛光去除率,同时可提高4H-SiC衬底的表面抛光质量.     

LBO晶体超光滑表面抛光机理

胶体SiO2抛光LBO晶体获得无损伤的超光滑表面,结合前人对抛光机理的认识,探讨了超光滑表面抛光的材料去除机理,分析了化学机械抛光中的原子级材料去除机理.在此基础上,对胶体SiO2抛光LBO晶体表面材料去除机理和超光滑表面的形成进行了详细的描述,研究抛光液的pH值与材料去除率和表面粗糙度的关系.LBO晶体超光滑表面抛光的材料去除机理是抛光液与晶体表面的活泼原子层发生化学反应形成过渡的软质层,软质层在磨料和抛光盘的作用下很容易被无损伤的去除.酸性条件下,随抛光液pH值的减小抛光材料的去除率增大;抛光液pH值为4时,获得最好的表面粗糙度.     

影响化学机械抛光4H导电SiC晶片表面质量的关键参数研究

选用二氧化硅抛光液抛光4H导电SiC晶片表面,探究影响SiC晶片表面质量的关键参数,获得更高的去除效率和表面质量.实验结果表明,SiC表面的氧化是氢氧根离子和双氧水共同作用的结果.保持压力不变并增加氢氧根离子或双氧水的含量,SiC表面去除速率先增加后保持不变.在更大的压力下增加氢氧根离子的含量,SiC表面的抛光去除速率进一步增加.通过优化的抛光参数,SiC表面的抛光去除速率达到142 nm/h.进一步研究结果表明,保持化学机械抛光过程中氧化作用与机械作用相匹配,是获得高抛光效率和良好的表面质量的关键.表面缺陷检测仪(Candela)和原子力显微镜(AFM)的测试结果表明,SiC抛光片表面无划痕,粗糙度达到0.06 nm.外延后总缺陷密度小于1个/cm2,粗糙度达到0.16 nm.     

雾化施液同质硬脆晶体互抛CMP工艺研究

探究了雾化施液同质硬脆晶体互抛CMP工艺抛光单晶硅片的可行性,分析其材料去除机理.试验采用传统的化学机械抛光CMP和雾化施液同质硬脆晶体互抛CMP,使用三种含有不同成分的抛光液对硅片进行抛光,对抛光前后的硅片进行称重比较两种工艺方法的材料去除率;通过扫面探针显微镜观察硅片的表面形貌,对其表面粗糙度进行分析.使用雾化施液同质硬脆晶体互抛CMP工艺对硅片进行抛光时,硅片表面材料去除率随着抛光压力的增大而增大,抛光压力为9 psi时达到最大为711 nm/min,高于传统化学机械抛光的630 nm/min;对两种工艺抛光后的硅片进行扫描分析得出雾化施液化学机械抛光工艺抛光后的硅片表面粗糙度为3.8 nm,低于传统化学机械抛光工艺的6.8 nm.雾化施液同质硬脆晶体互抛CMP工艺抛光硅片是可行的,优于传统化学机械抛光工艺,具有材料去除率高、抛光效果好、节约成本以及绿色环保的优点.     

不同磨料对蓝宝石晶片化学机械抛光的影响研究

本文制备了几种含不同磨料(SiC、Al2O3不同粒径SiO2)的抛光液,通过纳米粒度仪分析磨料粒径分布,采用原子力显微镜观察磨料的粒径大小.研究了不同磨料对蓝宝石晶片化学机械抛光(CMP)的影响,利用原子力显微镜检测抛光前后蓝宝石晶片表面粗糙度.实验结果表明,在相同的条件下,采用SiC、Al2O3作为磨料时,材料去除速率与表面粗糙度均不理想;而采用含1;粒径为110 nm SiO2的抛光液,材料的去除速率最高为41.6 nm/min,表面粗糙度Ra=2.3 nm;采用含1;粒径为80 nm SiO2的抛光液,材料的去除速率为36.5 nm/min,表面粗糙度最低Ra=1.2 nm.     

金刚石微粉对SiC机械抛光的影响研究

研究了金刚石微粉对碳化硅晶片表面机械抛光质量及去除率的影响.选取粒径均为W0.5～1μm、粒径分布和形貌不同的3种金刚石微粉,配置3种SiC单晶片机械抛光液.通过纳米粒度仪和扫描电镜分别测试了金刚石微粉的粒度分布和微观形貌.使用原子力显微镜测试了SiC晶片机械抛光后表面粗糙度.金刚石微粉的微观形貌越圆滑,粒径分布越集中,抛光后晶片的表面质量越好.金刚石微粉中单个颗粒的表面棱角有利于提高材料去除率.     

固结磨料研磨SiC晶片亚表面损伤截面显微检测技术

本文对采用截面显微检测法检测SiC晶片亚表面损伤时样品的制备、腐蚀液配方及腐蚀环境进行了系统地研究,并重点分析了固结磨料研磨SiC晶片(0001) Si面和(0001)C面亚表面损伤的深度及微裂纹构型.结果表明,采用腐蚀液配方为KOH:K2CO3 =20 g∶1 g,在420℃下腐蚀3min时亚表面损伤观测效果较好.在研磨压力为2 psi、金刚石磨粒粒径14 μm时,固结磨料研磨SiC晶片的亚表面损伤层深度约为2.6 μn,亚表面微裂纹构型有垂线状、斜线状、钩状、叉状、树枝状、人字状以及横线状.在相同的加工条件下,SiC晶片的(0001) Si面和(0001)C面的损伤深度基本相同.     

Ar气氛下退火处理对6H-SiC晶片表面结构的影响

本文对物理气相传输法生长的三片2英寸掺氮6H-SiC晶片,分别在不同温度下进行退火处理.采用原子力显微镜(AFM)对SiC晶片表面结构进行表征,研究了不同温度和偏角度对SiC晶片表面结构的影响.发现Ar气氛下高温退火处理可以在晶片表面形成规则的台阶条纹,说明Ar气氛下的高温退火处理对SiC晶片表面有一定的刻蚀作用.     

表面处理对CdZnTe晶片漏电流的影响

采用EDS、XPS、I-V等方法研究了Cd1-xZnxTe(CZT)表面处理工艺与晶片漏电流之间的相互关系。结果表明,机械抛光后的CZT晶片存在损伤层,采用5%BM溶液腐蚀可有效去除损伤层,得到光滑无划痕的表面,但腐蚀后晶片表面组成偏离化学计量配比,随腐蚀时间的延长表面呈现富Te现象,晶体表面漏电流随之增大1～2个数量级;采用KOH溶液对BM抛光后的晶片进一步腐蚀10min,可消除多余的Te得到接近于化学计量比的表面;采用NH4F/H2O2溶液对晶片表面进行钝化,XPS分析表明样品表面的Te0或Te2-被氧化成Te4+,形成高阻氧化层。I-V测试结果表明晶片经KOH+NH4F/H2O2溶液两步钝化后,表面漏电流相对于BM抛光后降低2～3个数量级,具有较好的钝化效果。     

Modelling of mechanism of agglomeration of KCl crystallization

The article presents an analysis into agglomeration during KCl vacuum crystallization. The theoretical and experimental investigations into the mechanism of agglomeration during mass crystallization result in an extension of the growth phenomena within the known model equations. The basis for this is essentially constituted by the collision model concepts of the theory of floculation in disperse systems. The parameters derived from the microprocess analysis (energy dissipation, content of solids, growth rate of individual grains) lead to model equations which are confirmed by laboratory and test trials.     

Relationship of Morphological Types of Dynamic Forms of Crystals

Crystallography Reports - The relationship of morphological spectra (sets of data on the morphological types of real polyhedral crystals and their probabilities under current physicochemical...     

Velocities of Disappearance and Lifetime of Faces of Growing Crystals

The formulae for absolute R_disap and relative R velocities of disappearance and lifetime τ of faces of growing crystals have been derived for stationary growth. It was shown that the quantities are determined by the relative growth velocity R_A/R_critA of the vanishing face A with respect to the critical growth velocity R_critA and by the geometry of a crystal expressed by the trigonometric functions of interfacial angles β and γ formed between face A and the adjacent faces. R increases and τ decreases with the increase in R_A/R_critA to certain limiting values. The calculations have been verified and illustrated by the experimental results for triclinic potassium bichromate (KBC) crystals. Results enable ones to predict values of velocities of disappearance and lifetimes of undesirable, supplementary faces of any real crystal.     

Development of Pauling's concepts of geometric characteristics of atoms

The evolution of the geometric characteristics introduced by Pauling and their dependence on the specific features of the structure and chemical bonds have been considered. The values of the covalent and van der Waals radii are given as well as their relationships and mutual transitions.     

Dependence of the parameters of equations of viscous flow on chemical composition of silicate melts

The temperature dependence of viscosity of silicate melts is discussed in the framework of the Avramov–Milchev (AM) equation. The composition is described by means of two parameters: the molar fraction, x, and the “lubricant fraction”, l. The molar fraction is the sum of the molar parts x_i of all oxides dissolved in SiO₂, the molar fraction of the latter being 1 ? x. It is shown that, with sufficient precision, two of the parameters of the AM equation can be presented as unique functions of the molar fraction. On the other hand, x is not sufficient to determine properly the reference temperature T_r , at which viscosity is η_r = 10¹³ [dPa.s]. Therefore, additional parameter, “lubricant fraction” l, is introduced. For each of the components, l_i is a product of molar part x_i and a specific dimensionless coefficient 0 ≤ k_i ≤ 1 accounting for the specific contribution of this component to the increased mobility of the system. It is demonstrated that, for l > 0, the reference temperature is related to the “lubricant fraction” l through the reference temperature T_r,SiO2 of pure SiO₂.     

Comparative analysis of two methods of calculation of the orientation of domain walls in ferroelastics

Two types of domain-wall equations are analyzed: the equations derived by the Sapriel method and the equations obtained by interface matching of the thermal-expansion tensor. It is shown that, for W-type domain walls, these methods yield the same equations. For W′-type domain walls, the equations obtained by different methods coincide for proper ferroelastics and differ for improper ferroelastics.     

A review of measurement of thermophysical properties of silicon melt

Measurements of thermophysical properties of Si melt and supplementary study of X-ray scattering/diffraction by the authors' group were reviewed. The values obtained differed variously from those of literature. Density was 2–3% larger, surface tension 20–30% smaller, viscosity up to 40% larger, electrical conductivity 8% smaller, spectral emissivity more or less in good agreement with literature values, and thermal diffusivity a few percent larger. An anomalous density jump was found near the melting point. Surface tension and viscosity also showed anomaly. A strange time-dependent change of density was observed over 3 h after melting. X-ray analyses suggested a slight change in local atom ordering, but showed no sign of cluster formation. An addition of 0.1 at% gallium caused the density jump to disappear, while that of boron caused no change. An EXAFS study of the former melt indicated a strong interaction between Ga and Si atoms as if molecules of GaSi₃ existed. The implications of the measured properties are a possibility of soft-turbulence in an Si melt in a relatively large crucible, a more complicated manner of intake of oxygen depleted molten Si from the free surface region to underneath the growing crystal, and a relaxation of the melt after melting arising from trapped gas species.     

Generation of crystal structures of heteromolecular compounds by the method of discrete modeling of packings

Within the method of discrete modeling of packings, an algorithm of generation of possible crystal structures of heteromolecular compounds containing two or three molecules in the primitive unit cell, one of which has an arbitrary shape and the other (two others) has a shape close to spherical, is proposed. On the basis of this algorithm, a software package for personal computers is developed. This package has been approved for a number of compounds, investigated previously by X-ray diffraction analysis. The results of generation of structures of five compounds—four organic salts (with one or two spherical anions) and one solvate—are represented.